Somdet Phra Borommaracha Thirat III (Thai: สมเด็จพระบรมราชาธิราชที่ 3) was the king of Ayutthaya from 1488 to 1491. Formerly Prince Borommaracha, Borommaracha III was the son of Trailokanat. Prince Borommaracha served as Trailokanat’s regent in Ayutthaya during his father’s campaigns against Lanna in the north. Trailokanat died in 1488 and Prince Borommaracha succeeded his father. Upon ascension, he moved the capital back to Ayutthaya. The throne of Sukhothai at Pitsanulok, however, was succeeded by his brother Prince Chettathirat.
His reign, however, was short. He sent Siamese armies to capture the Mon city of Tavoy in 1491 and died the same year.
He was succeeded by his brother Prince Chettathirat as Ramathibodi II.